<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
		<style>
			*{
				margin: 0;
			}
			.box1{
				width: 100%;
				height: 200px;
				background-color: red;
				position: fixed;
				z-index: 100;
			}
			.box2{
				padding: 30px;
				/* width: 500px; */
				height: 200px;
				background-color: yellow;
				border: 1px solid black;
				position:relative;
				/* top: 10px; */
				left: 10px;
				/* right: -10px; */
				bottom: 10px;
				
			}
			.box3{
				width: 500px;
				height: 200px;
				background-color:blue;
			}
			.box4{
				/* width: 300px; */
				height: 100px;
				background-color: green;
				/* 子绝父相 ,不考虑padding值*/
				position: absolute; 
				top: 10px;
				left: 50%;
				margin-left: -150px;
			}
		</style>
	</head>
	<body>
		<div class="box1">111111111</div>
		<div class="box2">
			<div class="box4">444444</div>
		</div>
		<div class="box3"></div>
	</body>
</html>
